Multiple fuse control mechanism in combination with thermoprotective signal system



lMarch 16, 1937. A, U BROUNE MULTIPLE FUSE CONTROL MECHANISM IN COMBINATION WITH THERMOPROTECTIVE SIGNAL SYSTEM Filed April 9, 1936 Patented Mar. 16, 1937 UNITED STATES PATENT OFFICE MULTIPLE FUSE CONTROL MECHANISM 1N COMBINATION WITH THERMOPROTEC- 2l Claims.

My invention relates to improvements in electric circuit overload devices, end has for one olaject tire provision of the combination of c standerd fuse, of the cartridge type, embracing e new 5 .fuse-element operative with e bimetallic thermo responsive means, to be installed os s, unit es o multiple iuse protection for electric lighting,

motors, and other electrical meci'iinery in branch circuits; or if used in main-feeder wiring protecl@ tico having su occessory assembled device, merruelly controlled cod mutually constructed for orcvvorning thru signal or ennunciotor against overloeds, unbalanced loods, or irregular 2e-eis loods in electricol circuits end meins.

Another ocject fol the invention is to provide for e. predetermined setting oi lilorete-d limits, the peeliood end maximum-demand use of electricity, end time' control o verving methods ci operation of eiectricel machinery in commer= 2.o cisl elects.

Another object or' the invention is to provide ineens for shooting tire vfeeirest point ou tile member icy the use of e iii-metal member.

il. further ooject is to `provide ineens for mais teintes trie sei-d loi-metal member :trom corotec1 ins or uniting tue two ports of o blown .elnotlier object 'ci' the invention, provides the means of o fuse protection ci tne verieirle lood clierecteristics in circuits, providing e comoinof 3@ tion luce :tor lieevy-dutv overleed storting cur= ci motors, end o lower ompereige fuse protection tor running" clierscteristics in motor cir= cuits, constructed one element.

.Another object oi tile invention is to provide e fuse element eed s, cicietcl unit joiritly cccseret= ine: in principle, in tine tiierrnel conductivity the iuse element, resulting in everleoie exo pension movement ci tlie loi-metal unit, to per mit e multiplicity uses thereof.

inotlier cloicct oi the invention, provides the use o e supporting insulated iibrous strip secured to the fuse, protecting" the molten fragmentary motel from comme; in contact with other metallic ports in the fuse, if end when seid fuse melts clue 45 to e short-circuit or dangerous overload, or orem vents seine from unnecessary warning Within inse-shell, and also provides e. ineens :Tor insulat-a edly separating the current iiow thru lose ii and when seme voletilizes with an overload or shortcircuited condition.

A. still further object of the invention provides the use oi e standard rellable cartridge ruse element, having e. new end novel construction of plurality sewerage-ratings in the seme fuse 55 clement operating jointly with a lai-metal unit (Cl. 206m-M3) secured to it; seme may be placed or interchanged in any standard cartridge-fuse, fuse-block, switchboard, cutout, service=switch, or standard motor control apparatus.

Fuses instelled in electric circuits and meinieeders ere denite protectives against overloads end short-circuits. However, such fuses fell in cert, iri tl'iot in practice, circuits and feeders are necessarily largely overiused or improperly fused, wel es o consequence electrical machinery, motors, transformers, and other electrical epgu "tenences ere frequently incapacitated, especieliy tlicse requiring varying starting end run ningeiood einpereges, the fuses being excessively oversized to ellovv greater storting empersges, resulting in burned out equipment, causing needless reolecemerits, repairs, and costly deleys. Tile merry oresent inventions and commercial devices electric current control, designed to interrupt eind dow or" current in circuits new in use etre only coordinated devices used in circuits necessarily overused.

is o new end novel invention for overload cire cuit prever-ities, l introduce e rellelole or rea ncvloloie type combination which will outometicsily compensate abnormal starting current reoiuremeuts, and also provide the necessary soie norme. fuse protection. Stenders". iuscs in sse ere rated iu emperes. ond its ruse element construction consists of o cut or notch, or te eririg' down to e reduced thickness in circuler:Irl s retiros in accordance with the designed are lilly invention consists of e use=e`iemcnt "osi/ing o, plurality ci notches but which notoires ore sized in thickness or circuler-mil of verielcle end intermediate sincere-ratings resulting in e multiple current resistance variability in tiie sorse useeelement; and it is operetive integrally wit i e lii=metel expansion unit or strip, engaged lo e syntloermel relationship to function in e multiple of epplicstious.

Toe invention is entirely tree from any eiectri cel reloys or electro-magnetic devices, and prom vides no ri'ieciionism which directs the dow of cura rent izo circuits, except es to the electrical rcsistence in the fuse element itseit. The ciistinoa tive features lie substantially in principle in the thermo-generation and heat-retention oi the fuse-element itself, end o co-acting thermo expensive bi-metei unit synthermoily related. Ii the invention loe used iu mein-feeder wiring ,or tectiou, the assembly of e, time-limiter and reguletor provides means whereby pre-arrangedly, end prior to tile fusing or melting of the fuseelement, o signal or annuncietor becomes operetive, and aiords the opportunity for the commercial plant attendant or management, and upon suitable signal indication to correct and reduce the overloaded or-critical situation in the system, and accordingly precludes the hazards of burn-outs and serious damage to the electrical equipment.

With the foregoing general explanation and otherdetails in view, the invention consists of a novel construction, combination and arrangement of parts as will be more specifically described and illustrated in the accompanying drawing wherein is shown an embodiment of the invention, but it is understood that modiiications, variations and alterations can be resorted to, which lie within the scope of the invention and ,the claims hereto appended.

In the accompanying drawing, Fig. 1 is a front elevational view of the device, showing a standard cartridge fuse, but with indicator attached.

Fig. 2 is a longitudinal sectional view thereof.

Fig. 3 is a sectional View on line 3 3 Fig. 1.

Fig. 4 is a fragmental sectional view showing the reserve plunger in position when the fuse has blown.

Fig. 5 is a fragmental sectional view of the attachable indicator mechanism. enlarged, and

Fig. 6 is a partial switchboard construction showing both individual branch circuits and the main feeder fuses provision, and the wiring arrangement of low-voltage current transformer and signal and annunciator system.

Referring now to the drawing in detail, I indicates the fuse shell constructed of fibre. Bakelite, or any refractorysubstance of non-metallic material, preferably cylindrical in form, comprising two end-ferrule caps Il, interiorly threaded or provided with other means to secure same to the cylinder shell I, and containing within said shell suitable means for making interiorly solid connection electrically and mechanically to a fuse-element I 5. If the fuse-is to be used in main-feeder circuit protection, said fuseshell It may be provided on its face withan insulated rotating regulator I2, comprising a screw 2d carrying an extended arrow-pointer I3, with suitable legends indicated at 3@ on said shell I@ over the arrow-pointer. The rotating regulator I2 lalso carries Aan extension-piece 32 having a screw terminal I4 to which is connected a wire 23 which is electrically connected to the timelimiting screw 24, the rotating of the latter creates a forward or backward movement depending upon the time-limit desirability of contacting with the bi-metal unit I6 at 33. The extension piece 32 is held in place against the fuse shell by any suitable meansat one end and it is provided at its opposite end with a hole 32, thru which time-limiter 24 is manually set and screwed thru the shell of the fuse, interiorly, to subsequently connect with the bi-metal member IB at 33. The construction of the time-limiter may be modiied in many adaptable forms provisioned with insulated members, having a. standard thread and may easily be engaged or disengaged with a screw thru the fuse-shell I0, for the purpose of interchanging the fuse from use in branch circuits without time-limiter engagement, or may be installed in main-feeder circuits-with time-limiter installed as an integral unit.

y With the installation of the time-limiter mechanism in the fuse, it becomes apparent that it is installed to make an electrical connection with the current in the system to the wire 23 for the cold thermostatically.

ycuit with an amperage, the fuse element having.

advenir purpose of connecting with a low-voltage transformer 26 (see Fig. 6) and then thru to annunciator 23 and signal 27. But since wire 23 is only one side of a connection, I provide the return wire 33 from any suitable neutral, or ground wire in the system which will connect to transformer 26, as shown at 38. The electrical connection of wire 23, thru 32, and then'thru time-limiter 243, will eventually complete' the electric circuit, if and when bi-metal I6 at 33 will expand or warp sulciently to Contact time-limiter 2li. When it has become so engaged electrically, the current passing thru it has the same potential or voltage as in the system, and with the neutral wire connection as described above completes the circuit to operate the annunciator and signal system for which this invention was designed. To suggest several variety wiring arrangements, I specically include low-voltage, transformer, and annunciator, the latter to indicate the particular side of line overloaded, but it is obvious that any electric signal, alarm, gong, pilot-light, or other indicating electrical devices may be direct-connected with the voltage in the line, tosignal the overloaded or dangerous condition in the system.

The fuse-element construction I5, as shown in Fig. 2, being a renewable type, has extendingfends or ears 3| and Sla to .engage mechanically and electrically to end caps II as-generally provided in rellable cartridge fuses-secured to said fuseelement is a separate -iiat non-conductive fibrous or hard-rubber strip 3.5, secured by rivets or otherwise as I8 and ISa which is intended to reinforce the fuse-element I5 in its entirety within the fuse-shell against warping, and it also -pro. vides means for preventing parts of theifusemetal from disintegrating and contacting.. the molten fuse with other parts of vmetal within fuse-shell in theevent of a short circuit in the system.

The fuse-element I 5 is also provided with al plurality of notches, or tapering downto a plurality of V shaped cutouts on the longitudinal side edges; such V notches having varied. circular-mil fuse ratings,.or ampere calibrations as indicated by I9, 20, 2 1, and v22 in Fig. 2.

-v By diierent sizes in ampere calibrationsUI mean a plurality of different (circular-mil) laxnpverage size construction in the same fuse-element.v The arrangement in the variable amperagecalibrations in the. .one fuse element is toibe made -in the most practicable form for` use in approximately the same regulatory manner as is now used in fuse protection of circuits and main-feeder installations. As indicated in Fig. 2,- the, upper i at 22, ampere rating. vIt is to be noted howeverg.A

the above is only suggestive, and.I may construct a variety of vamperage values in the same fusej element to meet any particular reguirement.

As is known, fuses installed in electric circuits being the weakest link in that circuit, will blowV at a dead-short or when the current is the same or greater amperage than the fuse rating. When the current is zero, the fuse-element is entirely As We subject the cira denite electrical ohmage or resistance, sets up a thermal condition, of and within ltself;-a heat corresponding to the amperages superimposed and prolongingly sustained in the circuit; the said heat being proportional to the increase or decrease ampere-load; and if an overload or critical condition be created larger than the rated amperes, the fuse when reaching a melting `temperature destructively fuses, snapping the circuit open.

As shown in Fig. 2, the bi-metal expansion strip I6 is secured at one of its ends to the fuse I5 by a rivet or fastening I1 and runs parallel and in close proximity thereto, within the fuse shell, said bi-metal expansion element overlapping snugly one or more variable amperage calibrations in the fuse-element. This bl-metal strip IS being of a certain thickness, consists of an alloy of two-metals having different coeiiicients of heat expansion; and the preferred bimetal I use is one of quick-responsiveness to heat treatment. Now the heat generated c superimposed in the fuse-element because oi an amperage ilowing thru it, faithfully reproduces itself in the thermostatlc bi-metal unit i6, which is welded or riveted at one end for instance snugly to it, and causes the loose-end 33 of the bi-metal to expand in a curved-movement therebeyond, and gradually expanding to the time-limiter 24 connected therethru to indicator I2 on outside of fus shell lll. The free end 33, will definitely warp in a curved movement, responding synthermally with the permeated heat and the heat retention by the fuse-element i5, or it will straighten itself out, flat, snugly and parallelly with the fuse element, when the current is reduced and the heat in the fuse approaches zero.

Pmerved for instant use, and movable thru a recess 36 in the strip 35 is an insulated plunger which is controlled by the tension of a spring 29 secured at one end thereof to the strip 35 by the rivet il. The reserve insulated plunger 3H is at right angles with fuse-element i5 on face side of strip 35, and is held normally rearward, in tension, between the resiliency, of the fuse element on one side of strip 35, and the spring 29 on the other. The reserve-plunger only becomes operative, automatically, when the amperage calibration at 2i, being the smallest and weakest of the whole range of amperage sizes in the fuse-element, breaks open. Ii a ruptured current or short-circuit takes place, it will automatically press thru recess 36, elevating the bimetal end a 33 away from its position; the fuse element at 2i now being broken away and volatilized with the short-circuit, oers no further resistance, and accordingly, allows the insulated plunger to function instantly. irrespective in what position the bi-metal i@ is held, either contracted (flat) and parallel with iuse element, or expanded outwardly (by the heat) in the space-gap toward time-limiter the reserveplunger will denitely separate at its lower or spring end and insulate the loi-metal from iurther contact with the remainder' ci the iuse. a prejudicial current be subjected in the circuit, the reserve plunger keeps the circuit open and interrupted, until a new fuse-element be replaced in the fuse.

The time-limiter 2li is so made that it may be readily inserted into or removed from the fuseshell l0. The elongated metallic threaded screw mechanism installed transversely thru shell it, can be manually moved forward or backward,

predeterminately, and is adjustable thereto with set-screw i2a. When the time-limiter 24 is ilxedly set, it of course provides a deiinite space-gap or zone, which is intended to gauge the time limit with which the bi-metal end 33 is ultimately to be connected, if and when the latter expands with the imposed heated condition therein. When the thermostatic bimetal has expanded, it bridges and contacts the end 33 with the limiter 24, connecting the electric current in the system, passing thru to extension piece 32 and then to wire 23,

'which as shown in Fig. 6 is connected with a lowvoltage transformer 26 continued to a signal 2l, and annunciator 2B; the return wire to complete the circuit being connected with the voltage in line or with any neutral or ground in the system.

In Fig. 6 there is shown a diagrammatic arrangement of a sectional open switchboard construction with the main feeder fuses together with branch circuit lines 39. Also wiring connections of low-voltage transformer 26, annunciator 28, and signal 2l. It will be noted that the latter` may be combined and installed at any remote place from the switchboard, found to be the most suitable location for the particular enterprise.

As stated the bi-metal expansion unit it becomes operative only. with the permeated heat in the fuse-element. .At cold temperature in the fuse-element or with an inconsequential current ilowlng thru it, the bi-metal d6 does not expand, and overlaps V 2@ and V 2 l, differently rated, but smaller amperage values than V i9 and V 22 and accordingly short-circuits or shunts these two under-disposed amperage ratings, the current passing thru the bimetal i6 simultaneously with the fuse at V i 9 and 22, the larger rated amperage Vs being now left to protect the circuit. The amperage ratings ci the latter two Vs are suinciently large to sustain an abnormal starting current load within the proximity of the heavy duty starting demands made of it; as for example, the starting of an alternating current motor requiring about 200% greater amperage than normal running current. In actual application, the starting of a motor causes a momentary sudden rush of a heavy current in the circuit, likewise impressed in the fuse, and were the two smaller amperage rated Vs at 26 and 2l not reinforced and short-circuited or shunted by the bi-metal it, they would necessarily blow at the starting instant. As can be apparently noted, the smaller rated amperage Vs being short-circuited and not ci a material consequence at the motor starting, the heavier rated amperage Js at i9 and 2t are now purposely overfused within safe limits of motor starting requirements.

it must be borne in mind, however, that the sudden abnormal starting current impressed in the circuit is only-momentary; and as the motor soon speeds up to normal current requirements, usually only a matter of seconds, it does not create an appreciable thermo-condition in the fuse, at the starting instant; nor sudciently to conduce and cause the curve-action of the bimetal unit it secured to it. However, as the current requirement of the motor soon becomes normal, it does cause a thermo status in the fuseelement, permeating a heat magnitude -in ratio with the sustained amperage in the circuit, and accordingly impregnates by conduction a synthermal relationship in the bi-metal it, causing it to form a warped curve-motion ita, as shown in Fig. 3. rI'he expanded curve-motion starts at 33 moving outward and away from fuse l5 to the hinged end at rivet l l, protruding into space-gap or zone toward limiter 24. As it does so, it separates itself from contact at 20 and 2|, the smaller rated amperages in the fuse. 'Ihe fuse now has become once again with the smaller rated amperages the major and predominating protection in the circuit; but it is the safest protection neces- 'sary to properly safeguard the electrical wiring and machinery in the line. If a prejudicial current be introduced suddenly while the motor is running, it is obvious that the smaller rated fuseamperages (now free and not short-circuited) will be rst to blow in the circuit. It must be noted,

that whereas the smaller rated fuse-amperag'e is Y the exact and true protection for the normal rating and requirements of the electrical machine, contradistinctive to the average present uses of fuses, with the detrimental over-fused consequences, my invention resides in an absolute improvement over present fuses or accessory'overloading devices now used in electrical circuits. It will also be noted that the installation of the variable fuse protection of this invention will not only give safer normal running current protection, but will also automatically compensate means for overloaded and abnormal starting characteristics of electrical machinery.

As another application in the use of this invention, it will be noted that same may be installed at switchboard for main-feeder protection of the entire electric load in a commercial plant. The many and irregular methods of electrical machinery operation aects the fuse-elementthermostatically. Fluctuating and variable temperatures in fuses at the main switchboard are caused by starting and stopping of motors; splitphasing; variable-impressed voltages; variable motor loads; partial openings in the line of motors; motors running with low bearings, the ro tor being out of center; increasing loads of spe- 40 cial electrical machinery, and other conditions too numerous to mention here. Fuses installed at the main-service' switch, cutout-block or switchboard are subjected to the entire load of the whole plant, circumventing not only the fluctuating conditions above mentioned, but the vast number and different kinds .ofmotors and machinery employed,` .and thevar-iable lighting and heating loadsin plants. :The thermo-responsivev ness of thesemain fuses registers a continuous heat rise and cooling effect, alternately corresponding as the load is, increased or decreased, and as the conditions be existent in the system.

In line with the above conditions, the installation and use of my invention tends to minimize the electrical malpractices or abuses in plants, and resides in the utilization of controlling at any pre-determined arrangement, a definite understanding with peak-load operating limits, and maximum-demand practices of electricity and electrical loads. The flexibility with which anyone inexperienced in the art may control pre-arrangedly any load limits, setting the indicator l2 and time-limiter 24, so as to permit, by the movement forward or backward of same to the desired definite limits with which bi-metal at 33 expanding with the load will connect with it. Connecting both bi-metal I6 and time-limiter 24 completes the circuit to automatically signal the attendant when the peak-load has been attained. As will be seen, this automatic operation requires little plant supervision and automatically registers signally a pre-determined peak-load, and accordingly enables the plant-management to systematize or regulate the electrical efllciency of his establishment.

Where it is desired to use my invention of multiple-fuse protection in single motor circuits, other than main feeder protection, (considering of course that the rated amperage of the motor is within the maximum proximity of fuse-rating) it will be seen that there be no requisite for indicator I2 and time-limiter 24 construction; and my invention resides in the iiexibility of disengaging or unscrewing this assembly in the fuse shell l0. 'I'hus it is noted that the device is interchangeable in use from main-feeder protection to branch circuit protection, and vice-versa; it offering the feasibility of multiple fuse protection, as well as the main control with the timelimiter assembled as shown in Fig. 3.

To summarize the various characteristics of my invention, it must be understood that same is not limited in use or construction or application; that itis interchangeable with any cartridge fuse, open fuse block, cutout, switch in branch-circuit or main feeder fuse protection; that as a fuse-element in combination with a thermo bi-metal function, it incorporates a multitude of uses; that same is' compactly constructed as a unit for quick replacements in standard cartridge -fuse shells overlying 'one surface of the said strip and shuntmetal expansible 'strip secured te the fusible strip, Y

ing-some of the said weakened areas and a strip of insulating material secured to the fusible strip at its opposite surface; 1

spaced apart areas of various electrical current carrying capacities vand a bi-metal expansible strip secured to the fusible strip overlying one surface of the said strip, and shunting some of the said weakened areas, the fusible and bi-metal strips being syn-thermal.

4. A fuse, comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas and .a

bi-metal expansible strip secured to the fusible strip, to shunt some of the said weakened areas. Y

vspaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, an insulating member secured to the fusible strip, and a spring pressed plunger of insulating material slidably mounted in the insulating member in line with the weakest area of the fusible strip for the purpose specified.

7. A fuse, comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, and indicator energizing contact means for contacting the free end of the bi-metal strip when same is heated and in warped position.

8. A fuse, comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, indicator energizing contact means for contacting the free end of the bi-metal strip when same is heated and in warped position, and a spring pressed plunger in line with the weakest area for preventing the return of the bi-metal strip to flat position when same is cold and the fusible strip has blown.

9. A fuse, comprising 'an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, a screw extending into the interior of the shell, in line with the free end of the bi-metal strip, and an electric contact in engagement with the said screw and an independent circuit closing lead wire secured to the said contact.

10. A fuse, comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, a screw extending into the interior of the shell, in line with the free end of the bi-metal strip, an electric contact in engagement with the said screw, an indicator lead wire secured to the said contact, a pointer carried by the screw and indicia on theA shell in operative relation to the pointer for the purpose specied.

11. A fuse, comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, a screw extending into the interior of the shell, in line with the free end of the bi-metal strip, an electric contact in engagement with the said screw, an indicator lead wire secured to the said contact, a pointer carried by the screw, indicia on the shell in operative relation to the pointer f or the purpose specified, and means for adjusting the inward extension of the screw.

12. A fuse, comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip in electric contact with the caps and having spaced apart electrically weakened areas, a bimetal expansible strip secured to the fusible strip, to shunt some of the said weakened areas, and an energizing indicator mechanism removably mounted on the shell and partly extending to the interior thereof in line with the free end of the bi-metal strip.

13. A reflllable type fuse for an electric circuit having variable starting and running characteristlcs, comprising in combination a fuse-element of multiple fuse areas of varying electric current 'carrying capacities. standard terminal-ends to adapt same for installation with a fuse reception means, and a bi-metal unit jointed to said fuseelement, the jointed combination fuse-element and bi-metal unit so synthermally operative that a current flowing thru the circuit will permit the sequence: (1) heavy duty fuse protection for the abnormal momentary-excessive starting current requirement, and (2) the smaller normal-running fuse protection in fuse-element for the normally sustained current requirement of a circuit, the said sequence maximum and minimum fuse-strength and resulting combinations at the different starting and normal-running intervals varying with the permeated and sustained thermic condition of both fuse-element and bi-metal unit, mutually and synthermally combined.

14. A refillable type fuse for an electric circuit having variable starting and'running characteristics, comprising in combination a fuse-element of multiple fuse areas of varying electric current carrying capacities, standard terminalends to adapt same for installation with a fuse reception means, a bi-metal unit jointed to said fuse-element, the jointed combination fuse-element and bi-metal unit so synthermally operative that a current flowing thru the circuit will permit the sequence: (1) heavy duty fuse protection for the abnormal momentary-excessive starting current requirements, and (2) the smaller normal running fuse protection in fuse element for the normally sustained current requirement of a circuit, the said sequence maximum and minimum fuse-strength and resulting combinations at the different starting and normal-running intervals varying with the permeated and sustained thermic condition of both fuse-element and bimetal unit, mutually and synthermally combined,

and means operatively associated with the bi metal unit which when contacted by the said bie metal unit will energize a signal indicator.

15. A fuse, comprising a fuse element having a plurality of fuse areas of varying amperage ratings, and a bi-metal strip secured to the fuse element to shunt some of the said areas when the bimetal strip is substantially cold.

16. A fuse comprising a fusible strip having spaced apart areas of varying electrical current carrying capacities, and a bi-metal expansible strip secured to the fusible strip overlying vone surface of the strip and shunting some of the said areas.

17. A fuse comprising a fusible strip having spaced apart areas of varying electrical current carrying capacities, and a bi-metal expansible strip secured to the fusible strip overlying one surface of the strip and shunting some of the said areas, the current passing through the said areas creating a rise in temperature causing the bi-metal strip to warp away from the fusible member. f

18. A fuse comprising a fusible strip having spaced apart weakened areas, and a bi-metal expansion strip secured to the fusible strip and shunting some of the weakened areas, the said bi-metal and fusible strips being syn-thermal.

19. A fuse comprising an insulating cartridge shell, metallic caps at each end thereof, a fusible strip having spaced apart areas of varying electrical current carrying capacities, and a bi-metal expansible strip secured to the fusible strip overlying one surface of the strip and shunting some of the said areas.

strip having spaced apart areas of varying electrical carrying capacities, and a bi-metai expansible strip secured to the fusible strip overlying one surface of the strip and shunting someof the said areas, the current passing through the said areas creating a rise in temperature causing the bi-metal strip to warp away from the fusible member, the said bi-metal and fusible strips being syn-thermal. 

